The correct option is
C Sorry to keep you waiting.
Option A: The expression, 'Thanks for everything' is an expression of gratitude appreciating the listener for all the help that he/she has done. In the given sentence: Dill is complaining that he has been waiting for Dina since 5 p.m. In this situation, thanking Dill for everything is not an appropriate response. Hence, this option is incorrect.
Option B: 'The expression, 'I can't be bothered', means: 'I don't care much for this as I have other important things to do'. Such a response to Dill would be rude and inappropriate. Hence, option B is incorrect.
In option C, Dina is apologising to Dill for having kept him waiting for a long time. This is the most appropriate response. Hence, option C is correct.
Option D: The expression, 'Just kidding!' is used to indicate that a statement is not to be taken seriously. This is not an appropriate response to someone who has been waiting for you for a long time. Hence, this option is incorrect.